生产者线程和消费者线程——腾讯面试题

[MM22GG]

8. 实现一个队列。
队列的应用场景为：
一个生产者线程将int类型的数入列，一个消费者线程将int类型的数出列

哪位高手可否给出 C++　的代码程序，谢谢。

[cd2108006026]

我对UNP的例子改了一下，支持多个生产者多个消费者

#include <pthread.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#define SIZE 50000
#define MAXTHREADS 10
struct
{
	int value;
	pthread_t tid;
} buf[SIZE];
struct
{
	pthread_mutex_t mutex;
	int index;//生产者使用，索引buf位置
} shared = { PTHREAD_MUTEX_INITIALIZER, 0};
struct
{
	pthread_mutex_t mutex;
	pthread_cond_t cond;
//	int num; // num of elems to be consumed, by p-c
//	int consumed;// num of elems already be read, only by consumer
	int ready;//在该索引及之前的元素可以消费 
	int consume;//消费者将要消费的元素下标
} nready = {PTHREAD_MUTEX_INITIALIZER, PTHREAD_COND_INITIALIZER, -1, 0};

void *produce(void *arg)
{
	for (;;)
	{
		usleep(1);
		pthread_mutex_lock(&shared.mutex);
		if (shared.index == SIZE )
		{
			pthread_mutex_unlock(&shared.mutex);
			return NULL;
		}
		buf[shared.index].value = shared.index;
		buf[shared.index].tid = pthread_self();
		++shared.index;
		pthread_mutex_unlock(&shared.mutex);

		pthread_mutex_lock(&nready.mutex);
		++nready.ready;
		if ( nready.ready == nready.consume)
			pthread_cond_broadcast(&nready.cond);
		pthread_mutex_unlock(&nready.mutex);
		++(*(int *)arg);
	}
}
void *consume(void *arg)
{
	for (;;)
	{
		usleep(1);
		pthread_mutex_lock(&nready.mutex);
		if ( nready.consume == SIZE )
		{
			if (nready.ready != SIZE - 1)
			{
				exit(3);//error
			}
			pthread_mutex_unlock(&nready.mutex);
			return NULL;
		}
		while ( nready.consume < SIZE && nready.ready < nready.consume )
			pthread_cond_wait(&nready.cond, &nready.mutex);
		if (nready.consume == SIZE)
		{
			pthread_mutex_unlock(&nready.mutex);
			return NULL;
		}
		if ( buf[nready.consume].value != nready.consume)
			printf("error: buf[%d]=%d, tid = %lu\n", nready.consume, buf[nready.consume].value, buf[nready.consume].tid);
		++nready.consume;
		pthread_mutex_unlock(&nready.mutex);
		++(*(int *)arg);
	}
}

int main(int argc, char *argv[])
{
	int i, nprod, ncons ;
	pthread_t tid_produce[MAXTHREADS], tid_consume[MAXTHREADS];
	int pcount[MAXTHREADS] = {0};
	int ccount[MAXTHREADS] = {0};
	if (argc != 3)
		perror("usage: a.out <#producer线程数> <#consumer线程数>"), exit(1);
	nprod = atoi(argv[1])> MAXTHREADS ? MAXTHREADS : atoi(argv[1]);
	ncons = atoi(argv[2])> MAXTHREADS ? MAXTHREADS : atoi(argv[2]);
	pthread_setconcurrency(nprod+ncons+1);
	for (i = 0; i < nprod; i++)
		pthread_create(&tid_produce[i], NULL, produce, &pcount[i]);
	for (i = 0; i < ncons; i++)
		pthread_create(&tid_consume[i], NULL, consume, &ccount[i]);
	for (i = 0; i < nprod; i++)
	{
		pthread_join(tid_produce[i], NULL);
		printf("produce thread %lu is done\n", tid_produce[i]);
	}
	for (i = 0; i < ncons; i++)
	{
		pthread_join(tid_consume[i], NULL);
		printf("consume thread %lu is done\n", tid_consume[i]);
	}
	for(i=0; i<nprod; ++i)
		printf(" producer %d \n", pcount[i]);
	for(i=0; i<ncons; ++i)
		printf(" consumer %d \n", ccount[i]);
	exit(0);
}